A Japanese patent document JP-A-H06-88733 discloses a navigation apparatus that learns a new road not registered in a map database based on the travel locus of the subject vehicle. As disclosed in the above document, the navigation apparatus generates and stores route data based on the travel locus of the vehicle when the vehicle has traveled an area outside of the registered area in the map database, for the purpose of “learning” the new road. Therefore, when a new road not registered in the map database is constructed, the new road is learned by the travel of the subject vehicle.
The map database used in the navigation apparatus of the above document is updated, the “learned” road that does not exist in the database before the update may be present (i.e., registered) in the database after the update. In that case, the data used for identifying the “learned” road becomes useless, thereby requiring a process that invalidates the useless data, for example. The navigation apparatus of the above-described type typically uses, as road identification data of the learned road, shape points coordinate data of the learned road, a link ID of the connecting road that is connected to the learned road, or the like. Therefore, the navigation apparatus may use those data, that is, the coordinate data and/or the link ID of the connecting road, to search for the road that corresponds to the learned road, and the data of the learned road may be invalidated when a corresponding road of the learned road is found in the updated database.
However, the link ID of the pre-update database may be different from the link ID of the post-update database for the same registered road, thereby making it impossible or impractical for searching a road in the post-update database based on the link ID of the pre-update database. Further, the shape point coordinates that approximates a two dimensional road having a width by a one dimensional line may not practically be used for the road search in the post-update database. That is, the coordinates may not match in the pre-update database and in the post-update database. Even if a nearby road that exists in the vicinity of a point indicated by the shape point coordinates is assumed as the learned road, that may not identify the corresponding road in an accurate manner, especially when there are more than one road in that vicinity.